Template wafer and process for small pitch flip-chip interconnect hybridization

ABSTRACT

A process is disclosed for high density indium bumping of microchips by using an innovative template wafer upon which the bumps are initially fabricated. Once fabricated, these bumps are transferred to the microchip, after which can be hybridized to another microchip. Such a template wafer is reusable, and thus provides an economical way to fabricate indium bumps. Reusability also eliminates nonuniformities in bump shape and size in serial processing of separate microchips, which is not the case for other indium bump fabrication processes. Such a fabrication process provides a way to form relatively tall indium bumps and accomplishes this without the standard thick photoresist liftoff process. The described process can be suitable for bump pitches under 10 microns, and is only limited by the resolution of the photolithography equipment used.

REFERENCE TO RELATED APPLICATIONS

This is a divisional patent application of copending application Ser.No. 12/571,812, filed Oct. 1, 2009, entitled “Template Process for SmallPitch Flip-Chip Interconnect Hybridization.” The aforementionedapplication is hereby incorporated herein by reference.

GOVERNMENT INTEREST

The invention described herein may be manufactured, used, sold, importedand/or licensed by or for the United States Government.

FIELD OF THE DISCLOSURE

The disclosure relates to a process for fabricating high density indiumbumps based on a template wafer, and transfer of these bumps tohybridize microchips.

BACKGROUND INFORMATION

Devices that contain microelectronic components generally require atransfer of information from the chip to one or several other componentson the system. In many cases, these other components are notmonolithically fabricated on the same chip, where they could be easilyinterconnected through a variety of techniques. Instead, a highlyconductive layer sandwiched between two components is required totransfer information. One of the industry standard ways to do this it byflip-chip bump bonding. This technique requires the deposition of a softconductive material to be deposited on either one or both of themicrochips to be bonded. Once performed, the two components areoptically aligned in a piece of equipment called a hybrid bump bonder,or hybridizer. After this alignment process, the two chips are pressedtogether by the hybridizer. This pressure, sometimes with the additionof heat, causes a permanent bond of the two components due to adhesionof the soft conductive layer.

Like most things in the microelectronics industry, the pitch of theseflip-chip interconnects has gotten smaller over time. This small pitchmakes it increasingly difficult to hybridize two chips with a high yieldof successful bonds. In some cases, new technology has emerged thatallows for small pitch interconnection through vastly differenttechniques. However, for a variety of reasons, these techniques aregenerally not suitable when bonding together chips that are composed ofdifferent substrate materials. One example of this is in the infraredsensing industry, where the light sensing focal planar array composed ofHgCdTe grown on CdZnTe is hybridized to a read-out integrated circuitcomposed of Si. These devices are generally thermally cycled betweenroom temperature when they turned off to 77° K during operation. A largedifference in the thermal coefficient of expansion between CdZnTe and Sicauses the two microchips to expand and contract differently over thistemperature range. This places a requirement on the interconnects to besoft and relatively tall in order to conform to the stress caused bythermal cycling. Due to these requirements, indium is the preferredinterconnect material. As higher resolution focal planar arrays withsmaller pixels are produced, smaller pitch. In interconnects will berequired to transfer information to the read-out integrated circuit. Asthis pitch falls below 10 μm, current technology will become lesscapable of successfully hybridizing the two microchips.

SUMMARY

A process is disclosed for high density indium bumping of microchips byusing an innovative template wafer upon which the bumps are initiallyfabricated. Once fabricated, these bumps are transferred to themicrochip, after which can be hybridized to another microchip. Thistemplate wafer is reusable, and thus provides an economical way tofabricate indium bumps. Reusability also eliminates nonuniformities inbump shape and size in serial processing of separate microchips, whichis not the case for other indium bump fabrication processes.

In one aspect, a template wafer is disclosed for small pitch flip-chipinterconnect hybridization, comprising: a core Si wafer; a Ni layer on afront side of said Si wafer; an Al layer on said Ni layer on the frontside; a Ni layer on a backside of said Si wafer; an Al layer on said Nilayer on the backside; a nonconductive layer based onpolytetrafluoroethylene up to a thickness of 20 microns as a top surfaceof said Al layer of said front side; and a nonconductive layer based onpolytetrafluoroethylene on a back surface of said Al layer of saidbackside. Surface features are formed into said nonconductive layer ofsaid front side. Said surface features are either etched or recesseddown to expose said Ni layer on said front side to yield conductivefeatures capable of indium plating to form indium bumps uponelectroplating.

In another aspect, a template wafer fabrication process is disclosed,comprising: at least one of degreasing and removing an oxide surface ofa core Si wafer; depositing a Ni layer on a front side of said Si waferbased on evaporation or sputtering; depositing an Al layer onto said Nilayer on the front side based on evaporation or sputtering; depositing aNi layer on a backside of said Si wafer based on evaporation orsputtering; depositing an Al layer onto said Ni layer on the backsidebased on evaporation or sputtering; depositing a nonconductive layerbased on polytetrafluoroethylene up to a thickness of 20 microns to atop surface of said Al layer of said front side; depositing anonconductive layer based on polytetrafluoroethylene to a back surfaceof said Al layer of said backside; applying a baking procedure to removesolvents and/or smooth exposed surfaces upon depositing of at least oneof said nonconductive layers; and forming surface features on said frontside to expose at least said nonconductive layer underneath. Saidsurface features are either etched or imprinted down to expose said Nilayer on said front side, yielding conductive features capable of indiumplating to form indium bumps upon electroplating. The evaporation can beeither electron-beam or heated evaporation, and the sputtering can beeither AC or DC sputtering.

The fabrication process described provides a way to form relatively tallindium bumps and accomplishes this without the standard thickphotoresist liftoff process, which makes it nearly impossible tofabricate relatively tall bumps with a pitch under 10 microns. Thedescribed process is suitable for bump pitches under 10 microns and isonly limited by the resolution of the photolithography equipment used.Additionally, this process is capable of producing relatively tall bumpswith heights over 8 microns possible for 3 micron wide bumps at a 10micron pitch. Such a large aspect ratio is important when hybridizingtwo microchips composed of different substrates that experience somethermal cycling. This is due to the need for the indium bumps to complyto strain caused by differences in the thermal coefficient of expansionof the two microchips.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is provided in reference to the attacheddrawings, wherein:

FIG. 1 a shows an exemplary template wafer to illustrate a bump transferprocess;

FIG. 1 b shows such a template wafer in an exemplary electroplatingsetup;

FIG. 1 c shows an exemplary plating of a template wafer;

FIG. 1 d shows a plated template wafer ready for transfer of indium;

FIG. 1 e shows an exemplary transfer process with a plated templatewafer placed on a vacuum chuck;

FIG. 1 f shows a release of exemplary bumps from a template wafer;

FIG. 1 g shows a bumped microchip held on a vacuum chuck;

FIG. 1 h shows exemplary hybridized microchips;

FIG. 2 a shows exemplary layers fabricating a template wafer;

FIG. 2 b shows deposition, patterning and etching of an exemplary maskfor the top of a nonconductive layer;

FIG. 2 c shows an exemplary template wafer after etching;

FIG. 2 d shows an exposed under layer in an exemplary fabricationprocess;

FIG. 2 e shows an exemplary finished template wafer;

FIG. 3 a shows a fabrication of another exemplary template-waferembodiment;

FIG. 3 b shows fabrication of said another exemplary template-waterembodiment after etching;

FIG. 3 c shows fabrication of said another exemplary template-waferembodiment with defined isolation notches;

FIG. 3 d shows deposition, patterning and etching of an exemplary maskfor the top of a nonconductive layer of said another exemplarytemplate-wafer embodiment;

FIG. 3 e shows said another exemplary template-wafer embodiment afterthe etching and removal of a photoresist;

FIG. 3 f shows the completion of said another exemplary template-waterembodiment;

FIG. 4 a shows the fabrication of an exemplary imprinting wafer;

FIG. 4 b shows an exemplary patterned imprinting wafer with etchedtrenches;

FIG. 4 c shows an exemplary incomplete template wafer placed on a vacuumchuck for imprinting; and

FIG. 4 d shows an exemplary template wafer as imprinted.

DETAILED DESCRIPTION

An exemplary indium bump transfer process is outlined in FIG. 1. Anexemplary template wafer as fabricated is shown in FIG. 1 a. Details ofthis process are discussed below. Such an exemplary template wafer iscomprised of a conductive core layer 101 and nonconductive layers 102,103 deposited and defined upon both sides of it. The top nonconductivelayer 102 is based on polytetrafluoroethylene (PTFE) as indium does notstick well to it. The dimensions of this wafer can be at least as largeas the dimensions of the area to be bumped on the microchip.

After the fabrication step, the template wafer is placed in anelectroplating setup FIG. 1 b. The electroplating setup includes a powersupply 103 that has the capability to run in a constant current mode.One such power supply is the Agilent 3616A. The positive terminal of thepower supply 104 is electrically connected to one terminal of an ammeter106 to monitor current being provided by the power supply. One may usethe Fluke 8845A digital multimeter operating in ammeter mode. The otherterminal of the ammeter is electrically connected to the anode 107. Inan exemplary embodiment, the anode is composed of high-purity indiumwith a purity of 99.99% or better. One face of the anode has a surfacearea that is equal to or greater than that of the template wafer. Thenegative terminal of the power supply 105 is electrically connected tothe template wafer 108. The template wafer is thus the cathode of theelectroplating setup. Both the anode and cathode are placed in anacrylic tank 109. The two electrodes are placed parallel to one another,separated by 5 centimeters. The tank is filled with an indiumelectroplating solution 110 so that the electrodes can be fullyimmersed. One can use the Indium Sulfamate electroplating solutionprovided by Indium Corporation of America. A sparging tube 111 is alsoplaced in the electroplating bath to improve mass transport by piping aninert gas, such as Ar or N₂.

Once the electroplating setup is connected, the power supply is turnedon and current is raised to initiate indium plating. Initiation ofplating 112 is shown in FIG. 1 c occurring only in regions where theconductive layer is exposed. The current is roughly in direct proportionto deposition rate, though current density should be kept between 108and 216 A/m², where the area is the surface area of indium platingregions. FIG. 1 d shows completion of plating when the indium overgrowsthe nonconductive layer 113. This overgrowth 114 should be on the orderof 1 to 2 microns.

The plated template wafer, shown in FIG. 1 d is now ready for removal ofexposed indium oxide and transfer of indium to a microchip. FIG. 1 eshows the beginning of this process. The plated template wafer 115 isplaced on the vacuum chuck 116 of a hybrid bump-bonder capable of micronresolution alignment. One such piece of equipment is the Suss MicrotecFC-150. The microchip 117 after removal of oxide from the metallizationpads is placed on the other vacuum chuck 118. The two wafers are alignedby the system so the indium 119 lines up with the metallization pads 120of the microchip. Once aligned, the hybrid bump bonder presses the two,with or without heat, resulting in a bond between the indium andmetallization pads. Upon releasing the two, the indium sticks to themetallization pads and releases from the template wafer, as shown inFIG. 1 f. The release is possible due to the small surface area ofindium at the conductive layer interface of the template wafer 121compared to that of the metallization pad interface of the microchip122. This is also possible due to the low adhesion of indium to PTFEthat allows it to easily transfer. The result is a set of indium bumps123 on the microchip 124.

FIG. 1 g shows the bumped microchip 125 held on the vacuum chuck of ahybrid bump bonder 126 after oxide removal from a remaining exposedindium, as in the above paragraph. Another microchip 127 which has theoxide likewise removed from its metallization pads is placed on theother vacuum chuck 128. The two wafers are aligned by the system so theindium 199 lines up with the metallization pads 130 of the secondmicrochip. Once aligned, the hybrid bump bonder presses the two, with orwithout heat, resulting in a bond between the indium and metallizationpads. FIG. 1 b shows the hybridized microchips after the release ofvacuum from the hybrid bump bonder.

Template Fabrication

The initial layers of an exemplary fabrication of the template wafer areshown in FIG. 2 a. In such an exemplary embodiment, a Si wafer 201 isthe core of the template wafer. The Si wafer can be degreased by dippingin, e.g., acetone, methanol, isopropyl alcohol, and deionized water fortwo minutes. The oxide surface of the Si wafer can then be removed bydipping in a 2% HF in deionized water solution for 1 minute. A 1 micronNi layer 202 is deposited on the front side of this wafer. One canperform deposition by a variety of techniques including (electron beamor heated) evaporation or (AC or DC) sputtering. This Ni layer willserve as the plating base where indium growth is initiated during theelectroplating process described above. A 200 nanometer Al layer 203 isthen deposited on the Ni layer by similar deposition techniques. Al ischosen because it sticks well to PTFE and will act as an adhesion layer.After deposition of these layers, a 1 micron Ni 204 layer followed by a200 nanometer Al layer 205 are deposited on the backside of the Si waferby the same deposition techniques. The purpose of these layers is tobalance stress on the Si wafer to keep it as flat as possible. The sumof these layers 201-205 comprises the conductive layer of the transferwafer 206.

In an exemplary embodiment, the top side nonconductive layer 209 isbased on PIPE (polytetrafluoroethylene) Teflon™ AF 1601S with 18% solidsprovided by DuPont de Nemours & Co. This layer is spun onto theconductive layer at spin speeds in the 3000-5000 rpm range. By dilutingthe Teflon™ 1691S in Fluorinert™ FC-770 provided by 3M, the thickness ofthe nonconductive layer can be spun-on as thick as 20 microns. Thethickness of this layer is chosen to be roughly 1 to 2 microns less thanthe desired final height of the indium bumps. After spin-on of thenonconductive layer, a baking procedure is necessary to drive outsolvents and allow for smoothing out of the surface. This procedure isas follows. The wafer is placed on a hotplate held at 1112° C. for 15minutes. The temperature is then ramped to 165° C. for 15 minutes. Atthis point, all of the solvents are driven out of the nonconductivelayer. Finally, the wafer is held for 30 minutes at 335° C. on thehotplate to smoothen out the layer. Afterwards, the wafer is allowed tocool. A backside nonconductive layer 208 is spun onto the backside ofthe wafer by the same procedure as for the top side layer. The bakingprocess is also the same, except the 335° C. step is omitted as surfacemorphology of the backside is not critical. The purpose of this layer isto stop any deposition of indium onto the backside of the wafer duringelectroplating.

FIG. 2 b shows the deposition, patterning and etching of an Al etch masknecessary to define the top side nonconductive layer 209. This processbegins with the deposition of 200 nanometers of Al 210. This layer canbe deposited by a variety of standard techniques including (electronbeam or heated) evaporation or (AC or DC) sputtering. The Al layer actsas the etch mask for the nonconductive layer because Teflon ™ AF 1601Shas a high etch selectivity over it during plasma etching. Al is alsochosen because it adheres well to Teflon™ AF 1601S. After the Aldeposition, a standard photolithography step is performed to definefeatures in the photoresist layer 211. These features will eventually bedefined down to the conductive layer by etching, so their dimensions arethose upon which indium plating will initiate to form indium bumpsduring the electroplating step.

To produce, e.g., 10 micron pitch bumps, these features can have a 10micron pitch and their individual size can be on the order of 2-4microns. This photolithography step can be the limiting factor of theminimum bump size and pitch attainable for such an exemplary templatefabrication procedure. Therefore, higher resolution photolithographytechniques should allow for bump sizes under 1 micron and pitches on theorder of a couple of microns. The Al layer is then etched, where exposedregions are etched, exposing the nonconductive layer underneath. Theetching can be performed either by chemical etching or plasma etching.One chemical etch that can be used is the PAN etch. This etch iscomprised of phosphoric acid, acetic acid, nitric acid, and de-ionizedwater in a 16:1:1:2 ratio held at 40° C. FIG. 2 c shows the templatewafer after etching of the Al etch mask layer and removal of thephotoresist by acetone bath of photoresist stripper.

After definition of the etch mask, the nonconductive layer 212 isdefined by a plasma etching step. Etching of PTFE, including Teflon™ AF1601S is achieved by a reactive ion etching process using a mixture ofAr and O₂ gases at several hundred eV. Obtaining proper sidewall angleis critical for good transfer of indium from the template wafer to themicrochip, as already discussed. The gas mixture should thus be tuned toobtain sidewall angles of roughly 70 degrees with respect to interfaceof the layers of the wafer.

Fabrication of the template wafer is completed by etching away theexposed Al under layer 213 by a chemical etch or plasma etch. Onceagain, the PAN etch described above could be used to for this purpose.FIG. 2 e shows the finished template wafer, where exposed Ni 214 willserve as the plating base upon which indium growth will begin duringelectroplating.

Second Exemplary Embodiment: Alternate Teflon™ Deposition Techniques

Another exemplary embodiment follows FIGS. 2 a-e. The following stepsoccur in the same manner as the initial exemplary embodiment: degreasingand oxide etching dip of the Si wafer, about 500 nanometer to 1 microntopside Ni deposition and 200 nanometer Al deposition, and backsideabout 500 nanometer to 1 micron Ni deposition and 200 nanometer Aldeposition. This exemplary embodiment uses a different set of techniquesto deposit the topside nonconductive layer 207 and backsidenonconductive layer 208 of FIG. 2 b. Instead of using spin-on Teflon™ AF1601-S to deposit these layers, PTFE can be deposited in a vacuumchamber onto the conductive layer of the transfer wafer 206 shown inFIG. 2 a. One can use either RF sputtering deposition or atomic layerdeposition (ALD) to perform deposition of PTFE. The thickness of thedeposition of the topside nonconductive layer can be chosen to beroughly 1 to 2 microns less than the desired final height of the indiumbumps. The thickness of the deposition of the backside nonconductivelayer can be chosen to be about 1 micron. This thickness is not criticaland only serves to cover the backside of the wafer to stop anydeposition of indium onto the backside of the wafer duringelectroplating. No baking steps are required after deposition.

After deposition of the PTFE nonconductive layers, fabrication proceedsas in the initial exemplary embodiment. This includes: deposition,patterning and etching of the 200 nanometer thick Al etch mask, plasmaetching of the topside nonconductive layer, removal of the 200 nanometerthick Al etch mask, and etching of the exposed 200 nanometer thick Alunder layer.

Third Exemplary Embodiment: Etching Notches

Yet another exemplary embodiment follows FIG. 2 a. The following stepsoccur in the same manner as the initial exemplary embodiment: degreasingand oxide etching dip of the Si wafer, about 500 nanometer to 1 microntopside Ni deposition and 200 nanometer At deposition, backside about500 nanometer to 1 micron Ni deposition and 200 nanometer Al deposition,deposition of the topside nonconductive layer by either of thetechniques described in the previous exemplary embodiments, anddeposition of the backside nonconductive layer by either of thetechniques described in the previous exemplary embodiments.

FIG. 3 a shows how fabrication proceeds for this exemplary embodiment.Just as in the initial exemplary embodiment, a 200 nanometer Al etchmask 303 is deposited on the nonconductive layer 301 by the sametechniques. After the Al deposition, a standard photolithography step isperformed to define features in the photoresist layer 304. Thesefeatures, unlike the previous exemplary embodiments, will not be used toetch down to the nonconductive layer 302. Instead, these features willbe used to define features that are etched partially down thenonconductive layer, which will be referred to as isolation notches. Thepurpose of these features is to delay touching of indium of adjacentplating regions of the template wafer. As previously set forth, indiumovergrowth above the nonconductive layer facilitates the indium transferprocess. As overgrowth occurs, lateral growth of indium occurs as well.These isolation notches will essentially isolate adjacent growth areasfrom one another by providing a longer path for lateral growth beforetouching occurs. The dimension of these features will depend on thepitch and size of bumps required. For 10 micron pitch bumps with anindividual size of 3 microns, e.g., 2 micron notches can be used. Asdiscussed in the initial exemplary embodiment, the size of thesefeatures is limited by the photolithography process involved. The Allayer is then etched, where exposed regions are etched, exposing thenonconductive layer underneath. The etching can be performed either bychemical etching or plasma etching as discussed in the initial exemplaryembodiment. FIG. 3 b shows the template wafer after etching of the Aletch mask layer and removal of the photoresist with acetone orphotoresist stripper.

After definition of the etch mask, the nonconductive layer 305 isdefined by a plasma etching step using the same techniques as thedescribed in the initial exemplary embodiment. The etching proceedsuntil roughly half of the thickness of the exposed nonconductive layeris exposed to form the isolation notches. FIG. 3 c shows the templatewafer after the nonconductive layer etching process to define isolationnotches 306 and removal of the Al layer by a chemical etch previouslydescribed.

FIG. 3 d shows the deposition, patterning and etching of an Al etch masknecessary to define the top side nonconductive layer 307. This processfollows the procedure of the initial exemplary embodiment, where a 200nanometer Al layer 308 is deposited, followed by definition of featuresin a photoresist layer 309 by a standard photolithography process andetching away of the exposed Al layer. FIG. 3 e shows the template waferafter etching of the Al etch mask layer and removal of the photoresistwith acetone or photoresist stripper.

After etching of the Al etch mask, fabrication proceeds as in theinitial embodiment. This includes: plasma etching of the topsidenonconductive layer 310, removal of the 200 nanometer thick Al etch mask311, and etching of the exposed 200 nanometer thick Al under layer 312.The completed template wafer is shown in FIG. 3 f.

Fourth Exemplary Embodiment: Imprint Fabrication

Yet, another exemplary embodiment follows FIG. 2 a. The following stepsoccur in the same manner as the initial embodiment: degreasing and oxideetching dip of the Si wafer, about 500 nanometer to 1 micron topside Nideposition and 200 nanometer Al deposition, backside about 500 nanometerto 1 micron Ni deposition and 200 nanometer Al deposition, deposition ofthe topside nonconductive layer by either of the techniques described inthe previous embodiments, and deposition of the backside nonconductivelayer by either of the techniques described in the previous embodiments.

This exemplary embodiment differs from previous ones in the way that thefeatures on the topside nonconductive layer are defined. Rather thanusing an etch mask followed by etching, this exemplary embodimentinvolves imprinting the topside nonconductive layer with featuresdefined on another wafer, to be called the imprinting wafer. The resultis that the features on the nonconductive layer will be a negative ofthe features defined on the imprinting wafer. The procedure for thisprocess is described below.

As shown in FIG. 4 a, fabrication of such an exemplary imprinting waferbegins with a Si wafer 401 of the same dimensions as the Si wafer usedas the core of the template wafer. A standard photolithography step isperformed to define features in the photoresist layer 402. In the end,these features 403 will be used to etch into the silicon wafer and thenimprinted into the nonconductive layer to form the mesas 215 shown inFIG. 2 e. The dimension of these features will depend on the pitch andsize of bumps required. If a 10 micron bump pitch is desired with 3micron bumps, these features will be roughly 7 microns because thesefeatures are the negative of the features imprinted in the nonconductivelayer.

FIG. 4 b shows such an exemplary patterned imprinting wafer afteretching trenches 404 in it. These trenches can be formed by placing thewafer in a plasma etching system, such as a reactive ion etching (RIE)system or inductively coupled plasma (ICP) etching system where amixture of O₂ and SF₆ etch away the exposed Si. Sidewall angle iscontrolled by the ratio of the two gasses and is controlled to etchsidewalls roughly 70 degrees with respect to the surface of theimprinting wafer. Etching proceeds until the etch depth is equal to thethickness of the nonconductive layer. After etching, the photoresistlayer is removed with acetone or photoresist stripper.

After completing the fabrication of the imprinting wafer, the imprintingstep follows, shown in FIG. 4 c. The incomplete template wafer 405,consisting of a conductive layer 406, an undefined topside nonconductivelayer 407 and a nonconductive backside layer 408, is placed on thevacuum chuck 409 of a hybrid bump-bonder capable of micron resolutionalignment. One such piece of equipment is the Suss Microtec FC-150. Theimprinting wafer 410 is placed on the other vacuum chuck 411. The twowafers are roughly aligned and heated past the glass transitiontemperature of the nonconductive layer. If this layer was formed usingthe first embodiment using Teflon AF 1601S, this temperature is 160° C.If this layer was formed using the second embodiment, this temperaturewill depend on the specific PTFE used. After heating, the two wafers arepressed together, held for several minutes, allowed to cool back to roomtemperature, and finally separated from one another. The result is anexemplary completed template wafer, shown in FIG. 4 d.

Using this process, it is possible to form the isolation notchesfabricated in the third embodiment. This requires an extraphotolithography and etching step in the imprinting wafer to formnegatives of the notches.

The invention has been described in an illustrative manner. It is to beunderstood that the terminology which has been used is intended to be inthe nature of words of description rather than limitation. Manymodifications and variations of the invention are possible in light ofthe above teachings. Therefore, within the scope of the appended claims,the invention may be practiced other than as specifically described.

What we claim is:
 1. A template wafer for small pitch flip-chipinterconnect hybridization, comprising: a core Si wafer; a Ni layer on afront side of said Si wafer; an Al layer on said Ni layer on the frontside; a layer on a backside of said Si wafer; an Al layer on said Nilayer on the backside; a nonconductive layer based onpolytetrafluoroethylene up to a thickness of 20 microns as a top surfaceof said Al layer of said front side; and a nonconductive layer based onpolytetrafluoroethylene on a back surface of said Al layer of saidbackside, wherein surface features are formed into said nonconductivelayer of said front side, wherein said surface features are eitheretched or recessed down to expose said Ni layer on said front side toyield conductive features capable of indium plating to form indium bumpsupon electroplating.
 2. The template wafer according to claim 1, whereinsaid Ni layers can range in thickness from 500 nanometers to 1 micronfor at least one of the front and back sides; wherein the Al layer canbe about 200 nanometers thick for at least one of the front and backsides; and wherein said surface features that are etched or recessedhave sidewalk that are angled by about 70 degrees with respect tointerface of the layers of the template wafer.
 3. The template waferaccording to claim 1, comprising isolation notches formed between saidsurface features to better isolate growth of adjacent indium bumps uponindium plating, wherein said isolation notches are either etched orrecessed partially into said nonconductive layer based on pitch and sizeof bumps such that for 10 micron pitch bumps with an individual size of3 microns, 2 micron notches can be used.